Add bash completion for `build --build-arg`

Signed-off-by: Harald Albers <[email protected]>

contrib/completion/bash/docker-compose

@@ -110,9 +110,17 @@ __docker_compose_services_stopped() {
 
 
 _docker_compose_build() {
+	case "$prev" in
+		--build-arg)
+			COMPREPLY=( $( compgen -e -- "$cur" ) )
+			__docker_compose_nospace
+			return
+			;;
+	esac
+
 	case "$cur" in
 		-*)
-			COMPREPLY=( $( compgen -W "--force-rm --help --no-cache --pull" -- "$cur" ) )
+			COMPREPLY=( $( compgen -W "--build-arg --force-rm --help --no-cache --pull" -- "$cur" ) )
 			;;
 		*)
 			__docker_compose_services_from_build